Comments (6)
lelit
commented on June 12, 2024
1
I'm closing this, as there isn't much I can do, other that inventing that other layer, a big effort with uncertain advantage.
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lelit
commented on June 12, 2024
Out of curiosity, can you show a sample statement that exhibits the problem?
In general, though, I'd prefer to avoid fiddling with parser's output... but let's see.
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tscholak
commented on June 12, 2024
Sure, no problem:
- Example where
rexpris adict:
SELECT count(*) FROM head WHERE age > 56[
{
"RawStmt": {
"stmt": {
"SelectStmt": {
"targetList": [
{
"ResTarget": {
"val": {
"FuncCall": {
"funcname": [
{
"String": {
"str": "count"
}
}
],
"agg_star": true,
"location": 7
}
},
"location": 7
}
}
],
"fromClause": [
{
"RangeVar": {
"relname": "head",
"inh": true,
"relpersistence": "p",
"location": 21
}
}
],
"whereClause": {
"A_Expr": {
"kind": 0,
"name": [
{
"String": {
"str": ">"
}
}
],
"lexpr": {
"ColumnRef": {
"fields": [
{
"String": {
"str": "age"
}
}
],
"location": 32
}
},
"rexpr": {
"A_Const": {
"val": {
"Integer": {
"ival": 56
}
},
"location": 40
}
},
"location": 37
}
},
"op": 0
}
}
}
}
]- Example where
rexpris alist:
SELECT avg(num_employees) FROM department WHERE ranking BETWEEN 10 AND 15[
{
"RawStmt": {
"stmt": {
"SelectStmt": {
"targetList": [
{
"ResTarget": {
"val": {
"FuncCall": {
"funcname": [
{
"String": {
"str": "avg"
}
}
],
"args": [
{
"ColumnRef": {
"fields": [
{
"String": {
"str": "num_employees"
}
}
],
"location": 11
}
}
],
"location": 7
}
},
"location": 7
}
}
],
"fromClause": [
{
"RangeVar": {
"relname": "department",
"inh": true,
"relpersistence": "p",
"location": 31
}
}
],
"whereClause": {
"A_Expr": {
"kind": 11,
"name": [
{
"String": {
"str": "BETWEEN"
}
}
],
"lexpr": {
"ColumnRef": {
"fields": [
{
"String": {
"str": "ranking"
}
}
],
"location": 48
}
},
"rexpr": [
{
"A_Const": {
"val": {
"Integer": {
"ival": 10
}
},
"location": 64
}
},
{
"A_Const": {
"val": {
"Integer": {
"ival": 15
}
},
"location": 71
}
}
],
"location": 56
}
},
"op": 0
}
}
}
}
]I'd prefer to avoid fiddling with parser's output
In general, I would agree. 👍
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tscholak
commented on June 12, 2024
In the pglast code, this is solved by case matching the kind: https://github.com/aiham/pglast/blob/master/pglast/printers/dml.py#L120
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lelit
commented on June 12, 2024
Thank you, I see. And what do you do on that? I mean, what would be your ideal way to deal with the polymorphic nature of that "value"?
The problem is that the "knowledge" of the "concrete shape" of the value must be obviously coded somewhere... one idea (without much thinking, really!) would be having a way to implement an higher level AST, that is, using a machinery similar to the "printers" that instead of a serialized, textual representation of the "low level" syntax would produce more usable/generic nodes...
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tscholak
commented on June 12, 2024
one idea (without much thinking, really!) would be having a way to implement an higher level AST
I think this is possible, but would require converting the A_Expr constructor into an A_Expr ADT with a set of constructors, one for each A_Expr kind. For instance:
A_Expr = A_Expr_Op(Val* name, Expr lexpr, Expr? rexpr)
| A_Expr_Between(Val* name, Expr lexpr, Expr rexpr1, Expr rexpr2)
| ...
something like that, where Type* means multiple cardinality, Type? means optional cardinality, and Type means single cardinality.
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